Modern Fish Live Fast and Die Young

An archaeological study by a WCS marine researcher in Kenya compares fish
communities from modern times with those from the Middle Ages. The scientist finds that
the modern fish are overwhelmingly smaller, lower on the food chain, and
shorter-lived.

The human life expectancy has trended up over the last
century. For fish, it’s a different story. A recent study by WCS researchers
found that fish communities in the 21st century live fast and die young.

The scientists compared fish recently caught in coastal Kenya with fish bones dug from ancient Swahili refuse heaps, in order to
understand how to rebuild current fisheries. They found that modern fish
communities contain more species with shorter life spans, faster growth rates,
smaller average sizes, and lower ranks on the food chain. By contrast, ancient
communities had a high percentage of top predators—species that prey on fish
and large invertebrates such as snails, sea urchins, and clams.

The cause of this downward trend is overfishing, which has impacted
the ecosystem in ways that may not be easily reversible, according to the
study. Over the centuries, fishing has greatly reduced or eliminated larger and
longer-lived species that were more commonly caught in the Middle Ages.

The study, which utilized more than 5,000 samples of ancient fish remains
dating between 750 and 1400 AD, approximately, appears in the current online
edition of the journal Conservation
Biology. WCS’s Tim R. McClanahan and Johnstone O. Omukoto authored the
paper.

“The ancient Swahili middens represent a time capsule of data, containing
information on the composition of the region’s fish assemblages and how human
communities influenced the marine environment,” said McClanahan, who leads
WCS’s coral reef research and conservation program.

The researchers also found that the number of fish bones in the middens peaked
between 1000 and 1100 AD before declining, while the bones of sheep and goats
become more prevalent in the higher levels of substrate, suggesting a shift in
human diet to domesticated animals.

“The archeological evidence demonstrates the incredible longevity of humanity’s
utilization of coastal fisheries, while emphasizing the critical need to
actively manage slower growing, longer-lived species within an ecosystem
approach,” said Dr. Caleb McClennen, Director of WCS Marine Programs. “The evidence from
Kenya aligns with findings from around the world that for millennia, humanity
has relied on the world’s oceans for our basic needs—but has more recently
failed to do so in a manner that also will sufficiently sustain that resource.”

Dr. McClanahan’s research has been supported by the John D. and Catherine T.
MacArthur Foundation and The Tiffany & Co. Foundation.